Sonar is not merely the art and science of detecting the existence of a sound in the sea; it is also the art and science of extracting the signal from the background noise, and of deducing from the signal the nature of its source. Considerable work has been done in automated signal extraction and categorization but, in the last analysis, the trained sonar operator is still the best signal extractor and categorizer. The signal must therefore be presented to the sonar operator in the best possible light. The prior art has not yet done this.